How do i know how much gas to put in?

[mikethomas]

I wonder if it possible for someone help me.I am currently installing Ac Equiptment and i do the gas weight as charge but what happens when i have stuff that i need to charge by had?Can someone tell me how i charge a system with the correct charge?

[BigJon3475]

Search for superheat and subcooling. there should be many threads regarding this.

[The Viking]

Nowadays, with mixed refrigerants and inverter driven compressors, most manufacturers will tell you to reclaim the system and then weigh the charge back in.

[squil]

If you want to know precisely the refrigerant charge, you need a good void fraction model applied to the condenser and the evaporator.
You can also roughly estimate it by assuming that a certain fraction (depending on the superheating or subcooling required) of the condenser and the evaporator are filled with liquid and the other part is filled with vapor. The volume of the tubes and of the compressor should also be taken into account.
This is the theory, but from my experience, the best thing to do after evaluating is to test the system while varying the charge.

[Chill doctor]

Reclain it, then recharge with new refrigerant by weight.
This is the only way to go, any other is just setting your self up for a call back mate.

The old fridge boys will still charge by feel, but ask the manufacturer, they are quite clear on this.

[marc5180]

As BigJon says check the superheat and subcooling and also the air off the indoor unit is a rough indication.